1 October 2003
A serious bug in the application of 1-D filters with gaps may cause
Sherpa to give incorrect fit results. This bug is present in CIAO 3.0
The algorithm that constructs the grid upon which models are evaluated
does not properly take into account filter gaps. If a user defines a 1-D
filter with gaps in it, then the calculation of the model predicted
values produces many more counts than what it is correct
in a bin at the edge of each gap.
Sherpa will NOT issue an error, but the results of fitting with this
filter will be INCORRECT.
NOTE that this bug applies *only* to 1-D filters. This bug DOES NOT
apply to 1-D continuous filters or any 2-D filters.
in the following filter, all the counts in the excluded region (7-8 Å)
will be included in the last bin of the 6-7 Å region:
sherpa> ignore allsets all
sherpa> notice 1 wave 6:7
sherpa> notice 1 wave 8:9
A typical instance of such a filter could be when trying to fit a
continuum excluding specific emission/absorption lines.
The only way to avoid getting silently erroneous results is to avoid
gaps in filters.
FIX: Will be available in a future CIAO patch
This archive was generated by hypermail 2b29 : Mon May 20 2013 - 01:00:06 EDT